It does indexing separately, but has a feature that lets you pass a search directly to Spotlight. I assume if you disable Spotlight, you'd just lose that feature and the rest of the app would function normally.
This won't be the case for all apps like this though. Alfred, which I use, relies wholly on Spotlight for indexing. If Spotlight stops working, so does Alfred.
EDIT: Just tested this. It seems like LaunchBar initializes itself with the Spotlight index. After that, I can't see where it's storing what it indexes, so I guess it's still depending on Spotlight, i.e adding to the Spotlight index, but doing so through it's own process.
If this is the case, even though it does its own indexing, it WILL be continuously dependent on the Spotlight index existing. You may not have to let Spotlight add to the index (via the
mds process), but you probably shouldn't delete the index.
They really don't make this clear on the product site or in the docs.